This invention relates to machine tools having hydro-mechanically stroked cutter spindles, and deals more particularly with a control system for such a machine.
The control system of this invention, in some or all of its aspects, may be applied to various different machines wherein a cutter or other tool is carried by a repetitively reciprocated or stroked spindle powered by pressurized hydraulic fluid. An example of such machine is a gear shaper as described in the U.S. patent application of Tlaker and Hazeltine filed simultaneously with this application. For the purpose of the following description, the machine tool with which the control system is associated is taken to be such a gear shaper and reference may be had to said Tlaker and Hazeltine application for further details of a hydro-mechanical mechanism for stroking the spindle.
The use of a hydro-mechanical means for stroking the spindle of a machine tool permits certain control flexibility not available with previous machines having spindles mechanically driven by linkages, racks and pinions, or the like and the general object of this invention is to provide a control system taking advantage of this control flexibility to provide a machine having significant performance and productivity improvements over prior machines.
Assuming that the machine in question is a gear shaper, such machine requires the incorporation of certain motions at controlled velocities within certain distances. Some of the important ones of these factors are: (a) the control of the stroking speed (stroke cycles/minute) of the cutter spindle to permit the cutting of workpieces of various materials and sizes, (b) the location of the cutter spindle stroking position in proper relationship to the workpiece, (c) the speed at which the workpiece and cutter spindle are rotated relative to one another to provide a rotary feed which determines the amount of material removed from the workpiece during each cutting stroke of the spindle and results in a certain cutting force, and (d) the rate at which the cutter axis is moved toward or away from the workpiece axis to feed the cutter into cutting depth and the distance it must travel to reach such cutting depth. A more particular object of the invention is, therefore, to provide a control system which conveniently satisfies the needs dictated by these factors.
In the gear shaper disclosed herein, the hydromechanical stroking mechanism is adjustable to provide the cutter spindle with selectively different stroke lengths and selectively different return speed ratios. A further object of the invention is, therefore, to provide a control system adaptable to accommodate such stroke length and return speed ratio changes.
Still other objects of the invention are to provide a control system to control the cutting force exerted by the cutting spindle to either maintain the cutting force within a selected maximum limit or to maintain a constant cutting force during a cutting operation, to control the hydraulic supply pressure and flow in response to existing cutting force and spindle stroking speeds to conserve energy and to protect against overspeed and hydraulic failure conditions, to minimize the time required for the non-productive return stroke of the spindle, to minimize the time required for the cutter to reach the desired depth cut during depth feed by providing a variable rate of depth feed which starts at a high value and diminishes to a lower value as the tool approaches the desired depth of cut position, and to provide a cutter spindle positioning means which permits the cutter spindle to be positioned in response to remote electrical inputs.
Other objects and advantages of the invention will be apparent from the following description and the drawings forming a part hereof.